What is the Acrosome?

Mary McMahon

The acrosome is a specialized organelle found on sperm cells. It wraps around the head of the sperm and contains enzymes designed to help the sperm penetrate the egg by breaking down the proteins in the egg's cell wall. In a process known as the acrosome reaction, the sperm cell fuses with the egg, releases the enzymes, and enters the egg to complete fertilization. This structure is of particular interest to fertility specialists, as problems with the acrosome reaction can cause fertility issues.

Acrosomes are specialized organelles found on sperm cells.
Acrosomes are specialized organelles found on sperm cells.

Viewed in cross-section, the acrosome looks like a thin cap covering the anterior section of the sperm. It forms during maturation of the sperm in the testes. As sperm approach the egg head first, they must fuse with the egg so the structure can break open, releasing the enzymes it contains. The enzymes soften the hard shell of the egg, making it possible for the sperm to penetrate by wriggling against the cell wall and slipping through the softened section.

The acrosome forms during maturation of the sperm in the testes.
The acrosome forms during maturation of the sperm in the testes.

Organisms that reproduce sexually rely on the acrosome to help their sperm enter the egg. Each sperm is slightly different, and success depends on the speed with which it reaches the egg, as well as the ability to successfully penetrate it. Once a sperm has managed to get beyond the shell of the egg, the tail drops off, as the sperm cell no longer needs to be motile. The fertilized egg can begin the process of multiplying and dividing, creating an embryo that will develop into a new organism with time.

In men with fertility issues, one test doctors may recommend is an assessment of the ability of the sperm to penetrate an egg. A sperm sample can be taken and exposed to chemicals that trigger the acrosome reaction in a specimen dish. If the sperm cell does not react as expected, this may explain why the man is having difficulty impregnating his partner. A doctor can discuss the options for the couple if they wish to continue trying to get pregnant.

It may be possible to get pregnant with the use of in vitro fertilization, where a care provider can assist the sperm with penetrating the egg and a viable fertilized embryo can later be implanted in the woman or a surrogate in a medical procedure. Couples may also consider the use of donor sperm that has been screened for viability in order to achieve a pregnancy.

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Discussion Comments


@indigomoth - It's easy to say that, but adoption can be almost as invasive and expensive as fertility treatments. And a problem with acrosome function isn't that big a deal in terms of fertility issues, after all, since they can manipulate the sperm and egg in a petri dish then implant it.

I actually think what's more of an issue is that fertility problems are actually fairly wide spread, not just in people, but also in other animals.

We should be looking for the overall cause of this decline as well as focusing on individual cures. If the decline continues we could all be in big trouble, since coupled with habitat loss it could impact on wild populations.

Of course, in a way, it's actually a good thing for human populations since those certainly don't need to increase any further.


@browncoat - I don't know if it would be a crisis if our fertility medicine wasn't better. I feel like it's still not all that great the moment. One of the options for dealing with faulty acrosomes is simply using someone else's sperm, for example.

I mean, they might deliver it in a clinical way now, but that's hardly high technology. That's a solution to male infertility that's been used for thousands of years.

And even if people couldn't use fertility medicine to ensure they have a baby (often a very invasive, expensive process) they could still adopt.

This world has no shortage of unwanted children in the world and I actually think it's a shame that there is such an emphasis on having biological children rather than adoptive children.


I've heard that fertility rates are dropping, particularly among men. There seem to be so many factors which can affect fertility, it's no surprise that a huge percentage of men seem to be less capable of getting their partners pregnant.

Just imagine how much more of a crisis this would be if fertility medicine hadn't been keeping up with the drop in fertility rates the way it has.

Even if you have an abnormal acrosome layer in your sperm you have other routes you can follow in order to have a child.

It's hard to imagine that even a hundred years ago they had no idea how sperm even worked and thought that it basically had a miniature baby in the head of it that was planted in the mother like a seed.

We've come a long way, I guess.

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